Princeton professor Naomi Ehrich Leonard is part of a team
conducting an unprecedented experiment with undersea robots that work
together without humans to make marine observations. Here, she prepares
the gliders for launch into Monterey Bay earlier this month.

Below left: The gliders move at a stately pace. "Sometimes
the current is three times the rate of the speed of the glider, so it
is a bit like a butterfly being tossed about in a windstorm," said
Leonard's graduate student Derek Paley. This means that keeping each
glider where it should be in relationship to all the other gliders is a
real challenge.

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Undersea robots glide into new realm of marine research

Posted August 24, 2006; 09:00 a.m.

by Teresa Riordan

This month in Monterey Bay, Calif., a fleet of undersea robots is
for the first time working together without the aid of humans to make
detailed and efficient observations of the ocean.

"It's thrilling," said Naomi Ehrich Leonard,
professor of mechanical and aerospace engineering at Princeton and
co-leader of the project. "The fact that six of these underwater
gliders are being coordinated with humans completely out of the loop is
unique." Leonard and co-leader Steven Ramp, of the Naval Postgraduate
School, briefed members of media Wednesday, Aug. 23, at the Monterey
Bay Aquarium Research Institute.

The oceanographic test site is yielding rich information about a
periodic upwelling of cold water that occurs at this time of year near
Point Año Nuevo, northwest of Monterey Bay. Upwelling events cause
plankton to "bloom," providing a rich source of food for the fisheries
and wildlife in the area.

But the project has potentially larger implications. It may lead to the
development of robot fleets that forecast ocean conditions and better
protect endangered marine animals, track oil spills and guide military
operations at sea. Moreover, the mathematical system that allows the
undersea robots to self-choreograph their movements in response to
their environment might one day power other robotic teams that explore
deserts, rain forests and even other planets.

"The work here is applicable to a wide range of problems," Leonard said.

In addition, the ability to coordinate autonomous vehicles -- a
challenge inspired by the grace of bird flocks and fish schools -- may
give biologists greater insight into the highly efficient behaviors of
animals.

"I find this work extremely exciting from two perspectives," said Simon
Levin, professor of ecology at Princeton who last year won the Kyoto
Prize for his use of mathematical models to understand the complex
patterns of the biosphere. "It offers potential payoffs in the
efficient and effective gathering of information. But it could also
give us a lot of insight into how animals organize themselves."

This month's experiment is unprecedented because so many robotic
vehicles are autonomously coordinating themselves for such a long
period of a time. While other researchers have created land-based
robots that self-coordinate for short periods of time, these underwater
robotic gliders are collecting data for a large-scale science
experiment, self-choreographing in three-dimensions, and doing so over
the course of an entire month.

Leonard has been working on the idea of biomimicry for at least a
decade, and she and her associates have demonstrated in computer
simulations and in short sea trials in 2003 that this self-choreography
could be achieved. But this is the first time they have demonstrated it
could work at the level of a full fleet with real robots at length.

The experiment is the centerpiece of a five-year program known as Adaptive Sampling and Prediction,
which is funded by the Office of Naval Research. Leonard's mathematical
system regulates the six underwater gliders, each measuring about 6
feet long and weighing more than 100 pounds. It determines what paths
the robots should follow to take the most information-rich samples, or
measurements, of ocean activity. As the ocean changes, automated
computer programs update the sampling strategy under the supervision of
the team.

Most of the scientists have not been on site during the actual field
experiment. Leonard herself has been in Princeton and New England
during parts of the experiment. The team collaborates while the work is
ongoing through teleconferences and through a virtual control room,
something like a chat room for the scientists. The researchers gather
in the virtual control room to share observations and make decisions
about changes to the field operation as it is under way. Leonard's
group includes graduate student Derek Paley and postdoctoral
researchers Francois Lekien and Fumin Zhang.

In contrast to typical ocean-observing systems, which are static, the
mobility of the gliders allows them to capture the dynamic nature of
the ocean, which is always shifting in time and space. Furthermore, the
gliders are coordinated into patterns to ensure that the measurements
they take are as information-rich as possible.

In a recent interview with the magazine New Scientist, Gwyn Griffiths,
who works on autonomous submarines at the National Oceanography Centre
in the United Kingdom, described the project's ability to update ocean
models so rapidly as "groundbreaking."

Inspired by the behavior of schools of fish, Leonard's group at
Princeton has created mathematical procedures that allow the gliders to
self-choreograph their movements in a series of rectangular patterns.
The patterns span a large volume of water that the scientists have
mapped just northwest of Monterey Bay (imagine a giant aquarium with
porous walls that is 20 kilometers wide, 40 kilometers long and ranging
from 50 to 1,800 meters deep).

The control algorithms allow the gliders to make day-to-day decisions
about how to alter their course without any input from humans. This
autonomy enables the gliders to stay in organized patterns even as they
are buffeted by strong currents.

The gliders have no propellers, thrusters or any kind of external
propulsion system. Instead, they are equipped with pumps that take in
or eject water, which makes the gliders sink or rise. As they go down
and up, the vehicles glide forward aided by fixed wings. They steer
with a rudder or, in some cases, simply by shifting their batteries
from one side to the other, which makes the glider bank. This
streamlined design requires a minimum of battery power and allows the
vehicles to remain at sea for weeks at a time.

These robots don't communicate directly with one another because
underwater communication is not practical given the distances between
the gliders. Each glider surfaces about every three hours in a
staggered pattern (only one glider surfaces at a time). When a glider
surfaces, it uses what is basically a cell phone modem connection, via
satellite, to transmit its location to a computer either at the Woods
Hole Oceanographic Institution in Massachusetts or the Scripps
Institution of Oceanography in California.

A computer in Princeton grabs the glider's new coordinates and ocean
current estimates through the Internet and then runs the software
designed by Leonard and her researchers, called the Glider Coordinated
Control System. The software acts as the gliders' collective brain.
Without input from humans, the software estimates where all the other
gliders are at that moment and spits out a new set of waypoints, or
destinations, for the glider that has just called in.

To do this, the software incorporates an important concept called
feedback. A glider uses feedback when it changes its direction in
response to where it is so that it can get to its next destination. The
part of Leonard's experiment that has never been done before is to use
feedback at the level of the entire fleet of gliders. Each glider
determines where to go in response not only to where it is but also in
response to where its neighbors are heading.

Although the field experiment in Monterey wraps up this month, the
project will continue through 2009. For the next couple of years,
however, the research can largely be conducted through analysis,
computer simulations and small-scale field experiments. "We have a
whole virtual-control setup now, with integrated tools and
collaborations already in place," Leonard said. "We will have a lot of
opportunities to build on what we have accomplished."